1. Field of the Invention
The present invention relates to a gas processing apparatus for an object to be processed which ensures that the temperature distribution within a surface of an object to be processed, such as a semiconductor wafer, is more even and thus improves the uniformity with which a film is formed thereon, and which also makes it possible to prevent corrosion of components such as power lines and terminals, and suppress the generation of particles.
2. Description of Related Art
During the process of fabricating a semiconductor device, film-formation processes such as chemical vapor deposition (CVD) or sputtering are performed to fabricate an integrated circuit on a semiconductor wafer of a material such as silicon (hereinafter referred to simply as xe2x80x9cwaferxe2x80x9d). To form a thin film uniformly over a wafer in such a film-formation process, it is necessary to heat the entire surface of the wafer to a predetermined temperature, then maintain that temperature.
One method of heating the wafer involves a film-formation apparatus that uses a ceramic heater. In this processing apparatus, a processing gas for forming a film is supplied into a processing chamber that is maintained at a vacuum, and a ceramic member which acts as a susceptor for the wafer and which also has a resistance heating member embedded therein is disposed below this processing chamber.
An enlargement of essential components of a ceramic member within such a processing apparatus is shown in FIG. 13, as disclosed in Japanese Patent Application Laid-Open No. 8-218172. Resistance heating wires 2 are embedded within a ceramic member 1, a pair of terminals 3 are connected to these resistance heating wires 2, and power lines 4 that are covered by insulating tubes 5 are connected to these terminals 3. The power lines 4 pass through a lower wall of the processing chamber and extend out to the exterior of the processing chamber.
The power lines 4 are surrounded by a sheathing bellows 6 made of a material such as stainless steel, an end piece 7 made of a material such as stainless steel is provided at an upper edge of the sheathing bellows 6, a ring member 8 of molybdenum is provided by gold-soldering to an upper edge of the end piece 7, and the ceramic member 1 is also gold-soldered to the ring member 8. A quartz protective tube 9 is provided outward from the sheathing bellows 6, and this protective tube 9 is connected to a gas supply pipe 10 for supplying an inert gas such as nitrogen to the interior of the protective tube 9, to purge it. A thermocouple 11 for measuring the temperature of the ceramic member 1 is housed within the sheathing bellows 6 and is led out to the exterior.
In this manner, the terminals 3 and the power lines 4 are surrounded by the sheathing bellows 6 and other components, and also an inert gas purges the interior of the protective tube 9, to ensure that the terminals 3 and the power lines 4 are not exposed to highly corrosive gases such as halogens. Instead, the terminals 3 and the power lines 4 are placed within an inert gas atmosphere, making it possible to prevent corrosion of the terminals 3 and the power lines 4.
When the interior of the processing chamber is cleaned with cleaning gases such as ClF3 and NF3, the interior of the quartz protective tube 9 is purged with an inert gas, so that the sheathing bellows 6 can be protected within the inert gas atmosphere without coming into contact with the cleaning gases, and thus corrosion of the sheathing bellows 6 can be prevented.
The insertion and gold-soldering of the molybdenum ring member 8 between the end piece 7 of the sheathing bellows 6 and the ceramic member 1 ensures that a material having a coefficient of thermal expansion that is close to that of the ceramic member 1 is in contact with the ceramic member 1, so that no cracks or other damage will occur in the connecting portions between the ring member 8 and the ceramic member 1 at the high temperatures used for film-formation processes (600xc2x0 C. to 700xc2x0 C.), for example.
In the above described technique, the molybdenum ring member 8 is inserted and gold-soldered between the end piece 7 of the sheathing bellows 6 and the ceramic member 1, which means that heat from the ceramic member 1 is transferred to the sheathing bellows 6 through this gold-soldered portion. Thus the surface temperature distribution of the ceramic member 1 becomes uneven and, as a result, the uniformity of the film formed during the film-formation process is adversely affected.
In addition, the configuration is such that the quartz protective tube 9 is provided and an inert gas such as nitrogen purges the interior of this protective tube 9, to protect components such as the molybdenum ring member 8, as described above. However, the gold-soldered portions of the molybdenum ring member 8 will become damaged by the thermal cycles during the film formation and the cleaning, and also these gold-soldered portions will be corroded by the cleaning gases, such as ClF3 and NF3, used in the cleaning. This means that the cleaning gases such as ClF3 and NF3 will leak into the ring member 8 through the thus damaged or corroded gold-soldered portions and be dispersed therein, causing corrosion and peeling of the molybdenum ring member 8 as well, and also causing corrosion of the terminals 3 and the power lines 4. As a result, there is a danger of particles being generated.
The present invention was devised in the light of the above described problems with the prior art, and has as an object thereof the provision of a gas processing apparatus which ensures that the temperature distribution within a surface of an object to be processed is more even and thus improves the uniformity with which a film is formed thereon, and which also makes it possible to prevent corrosion of components such as power lines and terminals of a heating means, and suppress the generation of particles.
In order to achieve the above object, a gas processing apparatus in accordance with the present invention comprises: a processing chamber; a susceptor provided within the processing chamber, for mounting an object to be processed; means for supplying a processing gas into the processing chamber to perform a predetermined process on the object; a resistance heating member embedded in the susceptor for heating the object; a power line, one end thereof being led out from a surface of the susceptor connected to the resistance heating member and the other end being extended to the exterior of the processing chamber; a metal sheath interposed between the surface of the susceptor and a wall of the processing chamber, for surrounding the power line so as to house the power line in an insulated state; and engagement means for connecting an end portion of the sheath adjacent to the surface of the susceptor to the surface of the susceptor.
Since this invention uses an engagement means to connect the sheath to the susceptor, it is more difficult for heat to escape to the metal tube from the susceptor that has been heated to a predetermined temperature by the resistance heater, than the prior-art connection provided by gold-soldering, making it possible to improve the uniformity of the temperature distribution over the surface of the susceptor and thus improve the uniformity of the processing of the object.
This sheath may be provided with an annular end piece at an end portion thereof adjacent to the surface of the susceptor, where this end piece is connected to the surface of the susceptor by the engagement means. The end piece may be configured of a cylindrical portion extending near the surface of the susceptor and a seating portion comprising a flange extending outward from the outer periphery of the cylindrical portion, where the engagement means passes through the seating portion. The annular end piece may be fixed to the susceptor by connecting means such as screw shafts alone in such a manner that the end piece is not in contact with the surface of the susceptor with a space formed between the end piece and the surface of the susceptor. Alternatively, the annular end piece may be fixed to the susceptor by connecting means such as screw shafts alone with the end piece in a line contact with, or in point or spot contact with the surface of the susceptor.
The engagement means may be configured of a screw shaft, where the screw shaft is inserted only partially into the surface of the susceptor, and a space is formed between the end piece and the surface of the susceptor. Thus the provision of this space makes it possible to reliably prevent heat from escaping from the susceptor to the sheath.
The seating portion may be provided with a hole through which the engagement means passes, where this hole has dimensions such that the engagement means passes loosely therethrough. The use of such a configuration makes it possible to permit thermal expansion of the sheath, making it more difficult for the connective portion between the sheath and the susceptor to be damaged, than the prior-art gold-soldering.
A corrosion-resistant tube made of a non-metallic material may be interposed between the surface of the susceptor and the wall of the processing chamber, surrounding the sheath with a space therebetween. This configuration makes it possible to protect the sheath from the highly corrosive cleaning gases during the cleaning. In addition, the cleaning gases do not leak into the interior of the sheath, preventing corrosion of the power lines and suppressing the generation of particles.
The configuration may also be such that an inert gas is supplied into the interior of the sheath. This ensures that the interior of the sheath is purged with the inert gas, making it possible to prevent the dispersion of the highly-corrosive cleaning gases back into the sheath. By allowing the inert gas to flow out from the sheath into the space between the sheath and the corrosion-resistant protective tube, the environment around the sheath can be made an inert gas environment, making it possible to prevent corrosion even further. By allowing the inert gas to flow out even further from the space between the sheath and the corrosion-resistant protective tube into the processing chamber, it is possible to completely prevent corrosion.